ADDITIVITY OF THE APPARENT AND TRUE ILEAL DIGESTIBLE AMINO-ACID SUPPLY IN BARLEY, MAIZE, WHEAT OR SOYBEAN-MEAL BASED DIETS FOR GROWING PIGS

Five pigs were fitted with a simple cannula in order to determine possible associative effects of cereal-based diets on apparent and true ileal digestibility of amino acids (AA). Barley (B), maize (M), wheat (W), soya-bean meal (SBM), B+SBM, M+SBM, W+SBM and protein-free (0.4% crude protein) diets were used. The digestibility values of the B+SBM, M+SBM and W+SBM diets were compared with those calculated from the values determined for the single ingredients and the proportion of the ingredients in the mixed diet. The calculated apparent digestibility tended to be lower than the observed digestibility, and there were significant differences (P < 0.05) between the observed and calculated values of all AAs in the B+SBM diet except for arginine, histidine, valine and glutamic acid. The differences (percentage units) obtained by subtraction of the calculated digestibility from the observed digestibility for the average of all the indispensable AAs in the B+SBM, M+SBM and W+SBM diets were 4.9. 3.5 and 1.2, respectively, for the apparent values, and 2.2, 0.3 and - 1.3, respectively, for the true values. It is concluded that true digestibility gives a more accurate estimate of the digestible AA supply in a mixed diet.